1. Field of the Invention
The present invention relates to installation tools for tangless wire formed inserts and, in particular, to an improved installation tool wherein the driving face of the insert engaging pawl member is modified to prevent the insert from moving axially in a direction away from the parent material during installation.
2. Description of the Prior Art
U.S. Pat. No. 4,528,737 and 4,553,302 describe tools for installing tangless wire formed inserts in holes formed in a parent material. The tool utilizes a pivotable pawl to engage a recess in the insert so that the insert may be screwed into the tapped hole.
A problem arises when the individual coils of the tangless wire formed inserts have a minimal cross section area so that the reliability of repeated successful installation is affected. 0n certain sizes the relationship of the thread pitches, internally and externally, and outside diameter often causes difficulty during the installation phase of the insert. Because of the reduction of the coil cross sectional area, increased flexibility of the lead entry coil may prevent it from aligning with the mating thread in the parent material. As the tool and the insert approach the installation hole, the insert is rotating to engage the lead mating thread. If the lead thread of the rotating insert engages the female thread in the parent material a short distance from the entrance, proper mating will take place and the installation cycle would then be normal. However, when this same rotating insert engages the first thread in the parent material a long distance from the entrance, the insert continues to rotate, its lead coil searching for the entrance thread as a downward pressure is simultaneously occurring. This downward pressure forces the lead coil on the insert to push back axially on the tool and then expand radially. The radial expansion occurs due to the flexibility of the lead entry coil as noted above, and does not allow installation because the major diameter of the insert has now expanded larger than the major diameter of the thread in the parent material. It then becomes impossible for the insert to have any chance to be installed. When this occurs the installation tool has to be stopped from rotation, reversed axially in direction and the insert removed and replaced with a new one.
What is thus desired is to provide an installation tool which prevents the axial movement of the insert lead coil when it abuts against the initial female thread in the parent material to allow installation of inserts having coils of minimal cross-sectional area.